"Big" and "little" forms of plaice vitellogenic and maturational hormones

Androgen-induced pseudo-hermaphroditic phenotypes in female Brevimyrus niger Günther 1866 (Teleostei, Mormyridae)

This paper explores the plasticity of sexually dimorphic characters in subadult female Brevimyrus niger, an African weakly electric mormyrid species. Thirty-five fish were exposed in a staggered fashion (five fish a week) to aromatizable 17α-methyltestosterone over a period of 7 weeks; 18 fish served as untreated controls. 17α-MT induced precocious vitellogenesis that mirrored the natural maturational process during seasonal ovarian recrudescence. At the same time, 17α-MT exposure resulted in complete masculinization of the females' anal fin support structure normally observed during rainy season in adult males. We discuss possible hormonal mechanisms acting along the brain-pituitary-gonad axis that would explain the occurrence of precocious vitellogenesis and the male-typical transformation of the female's anal fin ray bases. Our findings are relevant to commercial aquaculture as the use of 17α-MT in fish hatcheries can pose serious environmental issues.

Fundulus heteroclitus gonadotropins.5: Small scale chromatographic fractionation of pituitary extracts into components with different steroidogenic activities using homologous bioassays

Fractionation and characterization of gonadotropins (GtH) from Fundulus heteroclitus pituitary extracts were carried out using a biocompatible liquid chromatographic procedure (Pharmacia FPLC system). Chromatographic fractions were monitored for gonadotropic activities (induction of oocyte maturation and steroid production) using homologous follicle bioassays in vitro. Size-exclusion chromatography eluted gonadotropic activity in one major protein peak (Mr approximately 30,000). Anion-exchange and hydrophobic-interaction chromatography (HIC) yielded two distinct peaks of 17beta-estradiol (E2)- and 17alpha-hydroxy,20beta-dihydroprogesterone (DHP)-promoting activity with associated oocyte maturation. Two-dimensional chromatography (chromatofocusing followed by HIC) resolved pituitary extracts into two active fractions; both induced E2 synthesis, but one was relatively poor in eliciting DHP and testosterone production. Thus, using homologous bioassays, at least two quantitatively different gonadotropic (steroidogenic) activities: an E2-promoting gonadotropin (GtH I-like) and a DHP-promoting gonadotropin (GtH II-like), which has a lower isoelectric point but greater hydrophobicity than the former, can be distinguished from F. heteroclitus pituitaries by a variety of chromatographic procedures. This study complements previous biochemical and molecular data in F. heteroclitus and substantiates the duality of GtH function in a multiple-spawning teleost.

The brain–pituitary–gonad axis in male teleosts, with special emphasis on flatfish (Pleuronectiformes)

The key component regulating vertebrate puberty and sexual maturation is the endocrine system primarily effectuated along the brain-pituitary-gonad (BPG) axis. By far most investigations on the teleost BPG axis have been performed on salmonids, carps, catfish and eels. Accordingly, earlier reviews on the BPG axis in teleosts have focused on these species, and mainly on females (e.g. 'Fish Physiology, vol. IXA. Reproduction (1983) pp. 97'; 'Proceedings of the Fourth International Symposium on the Reproductive Physiology of Fish. FishSymp91, Sheffield, UK, 1991, pp. 2'; 'Curr. Top. Dev. Biol. 30 (1995) pp. 103'; 'Rev. Fish Biol. Fish. 7 (1997) pp. 173'; 'Proceedings of the Sixth International Symposium on the Reproductive Physiology of Fish. John Grieg A/S, Bergen, Norway, 2000, pp. 211'). However, in recent years new data have emerged on the BPG axis in flatfish, especially at the level of the brain and pituitary. The evolutionarily advanced flatfishes are important model species both from an evolutionary point of view and also because many are candidates for aquaculture. The scope of this paper is to review the present status on the male teleost BPG axis, with an emphasis on flatfish. In doing so, we will first discuss the present understanding of the individual constituents of the axis in the best studied teleost models, and thereafter discuss available data on flatfish. Of the three constituents of the BPG axis, we will focus especially on the pituitary and gonadotropins. In addition to reviewing recent information on flatfish, we present some entirely new information on the phylogeny and molecular structure of teleost gonadotropins.

Steroids involved with final oocyte maturation in the winter flounder

A number of androgens and progestogens including 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20-P) were examined in female winter flounder as possible maturation inducing steroids (MIS). During final oocyte maturation serum levels of testosterone (T) and 17 beta-hydroxy-5 beta-androsten-3-one (5 beta-T) peaking at over 200 ng/ml and pregnenolone (PE) at 40 ng/ml were the predominant steroids found from each major group. High levels of T and 5 beta-T were correlated with oocyte stages characterized by germinal vesicle migration. Of the PEs measured, maximum serum levels of PE, 3 beta,17 alpha-hydroxy-5-pregnen-20-one (17-PE) and 3 beta,17 alpha, 20 beta-dihydroxy-5-pregnene (17,20-PE) were found during later oocytes stages associated with germinal vesicle breakdown. Levels of 17,20-P, an established MIS in most fish, were almost non-detectable (less than 0.1 ng/ml serum) in females throughout all stages of final oocyte maturation. Incubations of ovarian follicles in vitro with physiological concentrations of T and 5 beta-T indicated that these steroids could induce all stages of final oocyte maturation. Similar in vitro incubations showed that 17-PE and 17,20-PE were only effective on germinal vesicle breakdown. The principal conclusions are that T, 5 beta-T and the PEs can be considered as MISs in winter flounder and the PE pathway predominates during the final stages of oocyte maturation in winter flounder in contrast to progesterones which predominate in other fish species, mostly salmonids, studies to date.

Growth hormone heterogeneity in American plaice pituitaries: isolation, characterization, and partial amino acid sequence

Growth hormones (GHs) have been isolated from pituitary glands of American plaice (Hippoglossoides platessoides), a marine flatfish, using affinity and gel filtration chromatography, followed by preparative polyacrylamide gel electrophoresis (PAGE). A bioassay based on serum triiodothyronine elevation in immature rainbow trout was used to monitor biological activity. These GHs originate from two molecular mass regions, 42K and less than 33K relative molecular mass (Mr), in their native state. The 42K Mr region yielded two forms of GH, which differ in terms of quantity and net charge as evidenced by native PAGE, a major variant with a relative mobility of (Rf) 0.22 and a lesser variant with Rf 0.28. The less than 33 Mr region has a single GH species with Rf 0.22. Upon sodium dodecyl sulfate-PAGE, without reduction, both GH variants from the 42K Mr region gave Mrs of 21K, while the GH from the less than 33K Mr region was 20K Mr, typical of monomeric vertebrate GHs. The proteins composing the 42K Mr region are proposed as GH dimers since they yield 21K Mr peptides. The less than 33K Mr region contains a GH monomer (20K Mr) in its native state. An amino-terminal amino acid sequence, identical for both the 42K and the 20K Mr Rf 0.22 forms, has good homology with other complete fish GH sequences near their carboxyl-terminal regions (between amino acids 130 and 196). The GH dimers (42K Mr) predominate in the plaice pituitary, contributing 93% of the total, of which 86% gives rise to the Rf 0.22 variant.

Isolation of sockeye salmon growth hormone utilizing serum triiodothyronine enhancement in rainbow trout to monitor biological activity

Growth hormone (GH) was isolated from sockeye salmon (Oncorhynchus nerka) pituitary glands using established techniques of affinity and gel filtration chromatography, and preparative polyacrylamide gel electrophoresis. The GH activity was followed throughout the fractionation procedure with a bioassay based on the increase of serum triiodothyronine (T3) in rainbow trout (Oncorhynchus mykiss), measured by radioimmunoassay (RIA). Amino-terminal amino acid sequence analysis and subsequent comparison with established GH sequences from other Oncorhynchus sp. were used to confirm the isolation of sockeye salmon GH (ssGH). The bioassay was sensitive to a dose of 55 ng of purified ssGH/g fish. Monomeric GHs, located in the carbohydrate-poor protein fraction, were the only pituitary components that elevated serum T3. Twenty-four hours after GH injection was an appropriate and practical time to blood sample, allowing completion of the bioassay, including RIA, in 3 days. The generic homology, between the source of pituitaries and the bioassay animals used in this study, should permit the bioassay to be useful during GH isolation from pituitaries of all Oncorhynchus sp.

Involvement of gonadotropin in the uptake of vitellogenin into vitellogenic oocytes of the rainbow trout, Oncorhynchus mykiss

The effects of two fully characterized, structurally distinct gonadotropins, GtH I and GtH II, on the uptake of vitellogenin (VTG) into oocytes of the rainbow trout, Oncorhynchus mykiss, were investigated both in vivo and in vitro. GtH I, injected into maturing vitellogenic females at a dose of 10 micrograms.kg body wt-1, increased the rate of [3H]VTG uptake into oocytes by more than two-fold, effectively doubling their rate of growth. Ovaries from females similarly treated with GtH II sequestered VTG at rates similar to controls. In vitro, GtH I stimulated VTG uptake in a dose-dependent manner. At a GtH I concentration of 100 ng.ml-1 and above, the rate of VTG uptake was significantly greater than that of the controls and at 1000 ng.ml-1 the rate of uptake was more than doubled. GtH II did not significantly increase VTG sequestration into isolated oocytes at concentrations up to, and including, 1000 ng.ml-1. These data provide the first evidence that GtH I has a primary function in stimulating VTG uptake and strongly support the contention that at least two functionally distinct GtHs occur in fish.

Purification and properties of pituitary gonadotropic hormone from Indian teleosts: freshwater murrel (Channa punctatus) and carp (Catla catla)

Gonadotropic hormone (GtH) from the pituitaries of two widely different Indian teleosts, a freshwater murrel and a carp, was purified by solvent fractionation, Sephadex G-100 gel filtration, affinity chromatography on concanavalin A-Sepharose (Con A-Sepharose), and immunoaffinity chromatography. Elution profile from gel filtration showed three peaks in both cases, peak I and II were clearly separated in murrel but not in carp. Peak II demonstrated strong GtH activity in both murrel and carp but this activity could also be detected in peak I and III of carp. TSH activity was restricted to peak I in murrel and was distributed in all three peaks in carp. Chromatography on Con A-Sepharose was useful in harvesting carp glycoprotein hormones, but gave no advantage in murrel. A pure homogenous GtH from murrel and carp could be obtained by using immunoaffinity chromatography. Polyacrylamide gel electrophoresis of murrel and carp GtH showed a single discrete band. Determination of molecular weight (MW) by Sephadex G-100 gel filtration indicated that murrel and carp GtH were 42,000 and 40,000 Da, respectively. SDS-polyacrylamide gel electrophoresis of murrel and carp GtH revealed two dissimilar subunits, alpha and beta. MW of murrel and carp alpha-subunits were 18,000 and 16,000 while those of beta were 27,000 and 26,000 Da, respectively. Comparison of electrophoretic patterns of murrel and carp GtH alpha and beta with ovine LH subunits reveal distinct teleostean GtH subunits.

Separation of gonadotropic fractions with different species specificities from tuna pituitaries

Eight different gonadotropic glycoprotein fractions were separated from the acetone-dried powder of yellow fin tuna pituitary glands by successive chromatographies on Superose 12 for gel filtration and Mono Q for anion exchange using the Pharmacia fast protein liquid chromatography system. This was preceded by preliminary separations using an ammonium sulfate precipitation method and affinity chromatography on concanavalin A-Sepharose. For biological characterization, we employed two radioreceptor assay systems, one using goby testis plasma membranes and silver carp GTH as the receptor and radioligand, respectively, and the other using testis plasma membranes of the yellow fin tuna and gonadotropin of the same species, respectively. We also employed two testicular cyclic AMP accumulation bioassay methods in vitro, one with the goby testis and the other with the mackerel testis. The least acidic fraction after Mono Q was further separated into four subfractions by rechromatography with Mono Q. They were strongly active in the tuna and mackerel assays but almost inactive in the goby assays. They were referred to as tuna-type tuna gonadotropin. In contrast, the most acidic fraction obtained after the first Mono Q was active in the goby assays but almost inactive in the tuna and mackerel assays. It was referred to as goby-type tuna gonadotropin. The intermediate fractions were active on both assays and are considered to be mixtures of tuna-type and goby-type gonadotropins. The reason for the presence of gonadotropin inactive to homologous species is discussed from the evolutionary viewpoint.

Pituitary thyrotropin and gonadotropin of coho salmon (Oncorhynchus kisutch): separation by chromatofocusing

Thyrotropin (TSH) and gonadotropin (GTH) were isolated from adult female coho salmon pituitary glands. After final extraction in acidic alcohol and precipitation in 85% ethanol, proteins were fractionated using gel filtration chromatography and chromatofocusing. Homologous bioassay systems were used to monitor bioactivity during the purification procedures. TSH activity was measured in vivo in coho salmon parr. GTH (steroidogenic) activity was determined in vitro using cultures of adult coho salmon ovarian follicles. Using these procedures, TSH and GTH activities were separated. TSH activity eluted as one major peak at pH 6.3 whereas GTH activity eluted as five major peaks at pH's 5.4, 5.0, 4.7, 4.3, and after 1.0 M NaCl on chromatofocusing. Molecular weights of the TSH and GTHs were estimated by gel filtration chromatography as 35 and 40 kDa, respectively. Like other vertebrate TSHs and gonadotropins, the coho salmon TSH and GTHs appeared to consist of two subunits. Coho salmon TSH and bovine TSH (bTSH) were equipotent in the TSH bioassay. The five coho salmon GTHs exhibited similar potencies in stimulating ovarian estradiol synthesis in vitro. Further biochemical analysis and tests for other gonadotropic activities are warranted to determine if these five GTHs are isoforms of one GTH or if they can be distinguished functionally in other GTH bioassays. Sufficient quantities of coho salmon TSH were isolated in this study for future studies of the hypothalamic-pituitary-thyroid axis in fish.

Pituitary extract of the ricefield eel Monopterus albus (Synbranchidae, Teleostei) exhibits gonadotropic activity in the classes Mammalia, Aves, Reptilia and Amphibia

Pituitary extract of the ricefield eel Monopterus albus demonstrated gonadotropic activity in mammals and non-mammalian vertebrates. Using the rat as the recipient, FSH activity was detected in Monopterus pituitaries in the HCG augmentation test and LH activity in the ovarian ascorbic acid depletion test. Cyclic AMP level in superovulated ovaries, ovarian lactate production and glucose uptake in vitro, plasma testosterone level in males, testicular enzymes, ventral prostate weight and other androgen-dependent parameters were stimulated after treatment with Monopterus pituitary extract. Testicular and ovarian 32P5+ uptake in the chick, testicular weight in the grass turtle Chinemys reevesi, and ovulation in the amphibians Xenopus laevis and Rana tigrina were enhanced. Both the FSH-like and LH-like activities in Monopterus pituitaries were sensitive to proteolytic enzymes and chemicals that attack the disulfide linkage, carbohydrate moiety, tyrosine, tryptophan and histidine residues. This constitutes the first report of dual gonadotropic activities elicited by a teleost pituitary extract in the mammal in vivo.

Progestogens, androgens and their glucuronides in the terminal stages of oocyte maturation in landlocked Atlantic salmon

Peripheral serum levels of free and conjugated steroids were correlated with seven terminal stages of oocyte maturation in female landlocked Atlantic salmon. Pregnenolone levels were maximal at stage 1, and there was a surge in testosterone after initiation of germinal vesicle migration. Testosterone remained high, above 25 ng/ml until ovulation, and its glucuronide was always lower than the corresponding free form. 17 alpha,20 beta-Dihydroxy-4-pregnen-3-one increased progressively from 0.71 to 68 ng/ml from oocyte stage 1 to 6, with the glucuronide predominating in stages 1 to 4 and the free steroid in stages 5 to 7. Thus, very low levels of free 17 alpha,20 beta-dihydroxy-4-pregnen-3-one were present when migration of the germinal vesicle was initiated but considerable free steroid was present at and after germinal vesicle breakdown. Negligible amounts of progesterone, 17 alpha-hydroxypregnenolone, 5-pregnene-3 beta,17 alpha,20 beta-triol were found in the serum during final maturation. In male salmon with expressible milt, 17 alpha,20 beta-dihydroxy-4-pregnen-3-one was present with a gradual increase of both free and conjugated form at the advent of spawning, suggesting that this steroid may also play a role in reproduction in male fish. The action of steroids in vitro on oocytes at various stages was consistent with conclusions based on blood levels.

Effect of carp gonadotropin (cGTH) and a fraction unabsorbed on concanavalin A-Sepharose obtained from cGTH on vitellogenesis in the hypophysectomized marine teleost Gobius niger

To investigate whether a differential potency on vitellogenesis exists between the carp gonadotropin (cGTH) and fraction I-cGTH (proteins from cGTH unbound on concanavalin A-Sepharose, which represent 5% of cGTH in weight), hypophysectomized Gobius niger were treated with the two hormonal preparations at the same level. Vitellogenesis was checked for synthesis of vitellogenin and yolk incorporation in the ovary by means of immunological studies and histological techniques (light and electron microscopy). In addition, increased synthesis of vitellogenin was induced by injection of estradiol 17 beta together with each gonadotropin to assess the action of the two hormonal preparations on vitellogenin incorporation. Oogenesis was enhanced by cGTH and fraction I-cGTH, and at the same dose levels both treatments produced a similar pattern of stimulation of vitellogenesis. Vitellogenin was found in all the blood samples of animals treated by the hormones (cGTH and fraction I-cGTH) alone. Vesicles of pinocytosis were detected by electron microscopy up to Stage IIIa of oogenesis. When a high synthesis of vitellogenin was induced by exogeneous estradiol 17 beta injections, the two gonadotropic preparations had similar effects in yolk incorporation. cGTH was not less potent than fraction I-cGTH in these processes even though the cGTH preparation contains only 5% of fraction I-cGTH. The contamination of cGTH by a small amount of material unbound on concanavalin cannot be solely responsible for the vitellogenic activity of cGTH which consists of 95% glycoproteins.

Plasma vitellogenin in landlocked Atlantic salmon (Salmo salar Ouananiche): isolation, homologous radioimmunoassay and immunological cross-reactivity with vitellogenin from other teleosts

Vitellogenin was isolated by affinity chromatography and gel filtration from landlocked Atlantic salmon plasma. Vitellogenin was labelled with iodine-131 using iodogen and an homologous radioimmunoassay was developed. There was poor immunological cross-reactivity with vitellogenin or plasma from other teleosts. Parallelism of the vitellogenin standard to the displacement by plasma of vitellogenic salmon allowed the assay to be used to evaluate the seasonal concentration profile of vitellogenin in female adult salmon. Extracts of liver or ovary from female Atlantic salmon also yielded displacements parallel to the vitellogenin standard in the assay.

A receptor preparation from testes of Salmo gairdneri (Richardson): in vitro binding studies with 125I-labeled hCG and trout pituitary proteins

A gonadotropin-receptor preparation from trout during full spermatogenesis known to bind 125I-hCG was used to test the ability of trout pituitary proteins to dislocate hCG from the receptors. From the proteins of male trout pituitaries chromatographed on immobilized concanavalin A, only the glycoprotein fraction was able to compete with hCG for the receptors. Unabsorbed proteins eluting in three fractions were radioiodinated and used as ligands. The fact that they were not taken up specifically by the receptor preparation, and the competition of the glycoproteins with 125I-hCG, is discussed in the context of the vertebrate's gonadotropic hormone system.

Immunocytochemistry of gonadotropic cells in the pituitary of some teleost species

An antiserum (anti-sGTH) raised against salmon gonadotropin (SG-G100) was tested on pituitary sections of Sarotherodon mossambicus, Carassius auratus, Anguilla anguilla (intact and estradiol-treated to induce the development of the gonadotropic (GTH) cells), Salmo trutta fario, and a protandric marine teleost (Sarpa salpa, Sparidae). Using an immunoenzymologic technique, anti-sGTH stained GTH and thyrotropic (TSH) cells in the species studied. Anti-sGTH stained the granulated GTH cells in S. trutta fario and S. salpa; the vacuolated cells remained faintly stained or unlabeled in most cases. The results are discussed in the light of cytological, ultrastructural, and biochemical data which suggest that two forms of GTH cells may be present in some teleost pituitaries.

Binding of 125I-hCG to rainbow trout (Salmo gairdneri) testis in vitro

Homogenates of maturing rainbow trout testes show specific binding sites for 125J-labeled hCG (= 125I-labeled hCG). The binding is competitively inhibited by unlabeled hCG and by a hypophyseal extract of rainbow trout. It could be demonstrated that the tissue 125J-hCG binding specificity is restricted to the gonadal preparation. The trout testis was characterized by determining affinity and capacity from Scatchard plot analysis giving a high constant of dissociation Kd 3.65 x 10(-10)/M and a low binding capacity of 0.88 x 10(-15) M/mg tissue. The test system is markedly dependent on temperature, incubation-time, and pH. The maximum binding was found at 37 degrees during 2 hr of incubation in a buffer of pH 7.5.